The proposed work will study the mechanisms by which drugs influence the transport of various compounds in the renal proximal tubule. Since transport across the renal tubule can be affected by events at the vasal-lateral and/or brush border membrane, transport studies will be conducted utilizing purified membranes from both aspects of the proximal tubule. In particular, the transport of uric acid and other organic acids, and the effects of numerous drugs on the transport processes, will be studied.